An increase in jellyfish could seriously impact on future fish stocks, a Devon professor has warned.

Martin Attrill, from the University of Plymouth's Marine Institute, said climate change is having an affect on the ecosystems of the open sea.

He said a study had revealed worrying implications for the North Sea, such as a growth in the jellyfish population which prey on young larval fish.

The professor's research included studying 50 years of plankton samples.

He related the patterns found to changes in the environment, in particular variations in the climate, as it moves between wet-warm and cold-dry conditions.

Major predators

His research found evidence that jellyfish are now more widespread than 20 years ago.

Professor Attrill said climate projections for the next 50 to 100 years expect the North Sea to become warmer, allowing jellyfish to become more common, thereby creating a potential problem for the world's seas.

"Firstly, jellyfish are major predators of animals in the plankton, including young larval fish," he said

"Additionally, very few other animals eat jellyfish, so a build-up will not provide food for the rest of the marine ecosystem.

"A combination of both means the findings are exceptionally important as climate-related changes in jellyfish in the North Sea could dramatically change the way the system is functioning."

In 2003, Peter Parks, a marine biologist who has studied jellyfish for more than 40 years, disputed global warming could be the cause of large numbers of jellyfish appearing in South West waters.

No one from the Department for Environment Food and Rural Affairs was available to comment on the professor's research.